Recent advance in neuroscience is making clear the natural shape of neurotransmitter, substance deeply related to memory in brain. It is said that some of these substances are neuropeptides containing prolines.
Recovery of the memory was reported by the dose of neuropeptide containing proline to experimental amnesia rat (See Science 211, 601 (1981)).
On the other hand, it is presumed that these neuropeptide-hormons shall be matabolized by cerebral endogenous peptidases. Especially, prolyl endopeptidase (EC, 3. 4. 21. 26) might take part in these metabolism closely (See J. Biochem., 94, 1179 (1983)).
From these facts, the studies were in progress that it should be possible to prevent or treat amnesia by inhibiting prolyl endopeptidase and suppressing the metabolism of neutrotransmitter. (See Protein, Nucleic acid and Enzyme 25(6), 513(1980); Nippon Nougei Kagaku Kaishi 58(11), 1147(1984); J. Neurochem., 41, 69(1983); ibid 42, 237(1984).)
For the purpose described above, several compounds were synthesized. For example, it is clear that N-benzyloxycarbonyl-glycyl-L-prolyl-chloromethane, N-benzyloxycarbonyl-L-prolyl-prolinal strongly inhibit prolyl endopeptidase (See J. Neurochem., 41, 69(1983)). More recently, it is disclosed that compounds shown below are effective for the above purpose.